1. Field of the Invention
The field of the invention is that of the methods for improving images from real-time and high dynamic low-light level digital video imaging systems. These imaging systems are notably used at night. There are numerous uses, in particular in the aeronautical field.
2. Description of the Prior Art
This type of system provides images which are not necessarily of extremely good quality, given the low luminance level of the scene. There are a certain number of image processing techniques for increasing the quality of the image, in particular by increasing or enhancing the contrast in the low grey levels.
The following contrast enhancement methods are noted:                enhancement based on global histogram rearrangement;        enhancement based on local histogram rearrangement;        enhancement based on frequency approaches;        enhancement based on illumination/reflectance approaches;        enhancement based on the “Retinex” human eye biological function.        
However, the images from the low-light level digital video imaging systems are particularly tricky to process insofar as they are at high resolution, highly dynamic, extremely noisy and delivered at a high rate. Therefore, the conventional image processing techniques mentioned above all have one or more of the following disadvantages:                degradation of the scenes having extremely wide luminous dynamics by the saturation of the overexposed areas of the scene;        large increase in the already present digital noise due to the low-light level environment;        appearance of processing “artefacts” restricting the scene comprehension;        reduction in the resolution of the initial image;        processing incompatibility with a high image rate real-time operation;        no preservation of the overall appearance of the scene.        